There are a number of energy storage systems that can be used for applications at different power scales.
At a small scale, battery and supercapacitor-type electrochemical systems can be used. These systems nevertheless have a certain number of disadvantages. Batteries represent environmental hazards and have a limited lifespan. Supercapacitors have insufficient energy density for most applications.
At a large scale, the storage of water in a reservoir at elevation is a good option. The water can be released at a chosen time and generate electricity by means of turbines. The main limitation of this technique is the small number of sites that can be adapted without heavy duty and costly work.
The storage of compressed air in an underground cavity (CAES=Compressed Air Energy Storage) is also an interesting option; it has been envisaged in patents, such as U.S. Pat. No. 4,885,912 to Gibbs & Hill, Inc., U.S. Pat. No. 3,996,741 to George M. Herberg, and in patent applications WO 93 06367 to Arnold Grupping and EP 106 690 to Shell International Research. However, the number of available sites is very limited and economically profitable implementation requires coupling with a combined cycle. This leads to very large plants, with major investments. In addition, this solution involves the consumption of fossil fuels, and is inefficient.
Finally, another alternative is hydro-pneumatic storage in which the compression of a gas is performed by pumping a liquid. However, this type of technology must be improved in order to increase efficiency and reduce costs.
Such a system, which uses a liquid piston system as a gas compression device is already known, in particular from document WO 2008 139267 to Ecole Polytechnique Fédérale de Lausanne. A sprayer or a grill integrated in the top portion of the chamber ensures the gas-liquid contact during the compression and expansion phases of the gas so as to maintain quasi-isothermal conditions. In this system, the thermal energy released during the compression phase is discharged into the atmosphere by means of an exchanger. This same exchanger serves to provide calories during the gas expansion phase.
This type of system, while satisfactory, nevertheless has some non-negligible disadvantages. Indeed, the efficacy of this type of storage remains limited in particular due to the energy loss constituted by the discharge of calories during the gas compression phase. In addition, the stored energy restitution phase is accompanied by a cooling of the liquid associated with the expansion of the gas. It is therefore necessary to expend a non-negligible amount of energy to ensure isothermal expansion of the gas.